Stand, in particular for surgical microscopes, having an energy storage element

ABSTRACT

The invention concerns a stand arrangement ( 1 ) having a particularly arranged energy storage element ( 7 ) with specific parameters, in particular a low spring progression. The static friction is thereby reduced to a minimum.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of the German patent application 102004 017 971.9 filed Apr. 12, 2004, which application is incorporated byreference herein.

FIELD OF THE INVENTION

The invention concerns a stand, in particular a stand for a surgicalmicroscope, having one or more energy storage elements. “Energy storageelements” are understood in general to be elements that are suitable forabsorbing an energy or force and delivering it again, or converting itinto a different form of energy, in defined fashion. Relevant in thiscontext are springs of mechanical, pneumatic, or hydraulic type or acombination of such types, or shock absorbers. Gas springs are primarilyused in stand construction, in particular for surgical microscopes, butsprings of the other aforementioned types are also implemented.

BACKGROUND OF THE INVENTION

In order to achieve a maximally space-saving stand configuration, standshaving energy storage elements dispense with a counterbalancing armconfigured as a counterweight, or even a counterweight that is locatedopposite the horizontal support, but instead make use of the energystorage element, which takes over the lever function of the horizontalsupport, in particular under the load of the microscope. Gas springsused for this purpose as energy storage elements comprise a cylinderthat is internally hollow and is divided by a piston into two pressurechambers. The piston is equipped with small holes (nozzles) throughwhich pressure equalization can take place only in delayed (“cushioned”)fashion. Because the cylinder represents a closed pressure system,pressure equalization takes place until the pressures in the twopressure chambers are the same.

Conventional stands with gas-spring bracing have proven successful, butare used only in stands that exhibit moderately homogeneous movement.Different types of bracing, for example the balance-likeweight/counterweight system, are used for stands that need to be usedover a larger movement space and/or with more convenient movementguidance.

Conventional gas-spring support systems in stands are interchangeabledepending on the load that is to be used, i.e. different gas springs areused for different loads. This is necessary because the working range ofconventional gas springs has insufficient bandwidth. The bandwidth ofthe various weights of the surgical microscope, depending e.g. onaccessories, must be distributed over gas springs of different strengthsso that a balanced-out state of the stand can always be guaranteed. Inother words: assuming, for example, a gas spring having a conventionallynarrow working range, if the surgical microscope hung on the stand wereone equipped with more accessories than provided for, and if it balancedout in a certain position and then departed from that balanced position,the horizontal support would then move automatically into differentpositions.

Conventional gas-spring-braced stands have the disadvantage that becauseof the so-called “cosine function” of the load lever effect of themicroscope along its vertical movement arc, the bracing effect that ispresent differs as a function of the angular position of the horizontalsupport with respect to the vertical support. The (lever) force on thegas spring acting as the supporting lever is also greatest with thestand in the pivot position in which the load is located farthest awayfrom the vertical support (the horizontal support and vertical supportform a right angle).

EP-B1-433 426 describes a compensating apparatus, having a gas spring asthe energy storage element, that encompasses an arc-shaped orkidney-shaped elongated guidance hole on the vertical support in whichthe proximal end of a piston rod is guided, while the cylinderconstituting the distal end of the gas spring is secured pivotably onthe horizontal support. (In the remainder of this Application,“proximal” means “toward the vertical support” and “distal” means “awayfrom the vertical support, toward the unattached end of the horizontalsupport”.) This construction with an arc-shaped elongated guidance holeis theoretically intended to prevent the hysteresis of the gas springfrom becoming disadvantageously perceptible. “Hysteresis” is understoodin general to mean the dependence of the physical state of an object onprevious states, based on a residual effect (remanence) after removal ofthe applied physical magnitude or force.

It has been found in practical use, however, that this configuration isdisadvantageous in that the proximal end of the piston rod does not movecontinuously in the arc-shaped elongated guidance hole but instead, whenused, jumps from one extreme position to the other in the manner of atoggle lever; for a user, this requires an additional movement acrossthe jumping point in order to achieve readjustment of the supportconditions in the arc-shaped elongated guidance hole.

SUMMARY OF THE INVENTION

It is thus the object of the invention to arrive at an improved systemhaving energy-storage-element bracing, in particular gas-spring bracing,that is adjustable to different loads on the one hand so as thereby toeliminate the interchanging of different gas springs for differentloads, and on the other hand in order to eliminate the disadvantageouscosine effect of the horizontal support under the load of themicroscope, or reduce it sufficiently that it is no longer an annoyance.The toggle-lever jump effect is also to be eliminated. At the same time,the energy storage element must meet the typical requirements for asurgical microscope stand, i.e. the energy storage element must becapable of absorbing a counterbalancing force of approximately 2000 N.Conventionally, however, such high-rated energy storage elements exhibita spring progression of approximately 18%.

These objects are achieved by the selection of an energy storage elementhaving a defined and selected spring progression of, in novel fashion,less than 10%, preferably less than 9% (conventional gas springs have,on average, 11-60%), preferably accompanied by the highest possibleenergy absorption. The latter is preferably approximately 2000 N. Thelowest possible spring progression value also guarantees a lowhysteresis, which has an annoying effect specifically in the smallmovement ranges that are typical of a surgical application. In otherwords, according to the present invention the static friction, whichplays a substantial role in the context of small movements of thehorizontal support, is kept as low as possible (less than 60 N), whilethe dynamic friction, which plays a role in the context of largermovements of the horizontal support, can assume any arbitrary andrelatively larger value. The reason is that the dynamic friction is ofsubordinate significance because large movements of the horizontalsupport are necessary only in the context of prepositioning operations,but not in the context of fine manipulation movements during surgicaluse.

Simultaneously or alternatively, these objects can be achieved by thefact that in novel fashion, instead of the conventional installation ofthe gas spring piston rod on the vertical support and of the gas springcylinder on the horizontal support, it is the gas spring cylinder andnot the gas spring piston rod that is articulated at the displaceablemounting point of the vertical support. The gas spring piston rod isthus, in novel fashion, preferably articulated as far out as possible atthe distal end of the horizontal support. On the one hand this reducesthe disadvantageous effect of the cosine function of the load, since theweight of the cylinder is shifted from the distal end of the horizontalsupport closer to the vertical support. An additional result is that asmaller annoying variable magnitude is present, which in novel fashionis no longer determined by a larger shiftable cylinder mass but insteadby a smaller shiftable piston-rod mass. On the other hand, a gas springof the greatest possible length exhibits better hysteresis properties(because of larger pressure chambers and, associated therewith, a lowerpotential pressure in the gas spring).

It is also preferred, for the sake of larger pressure chambers (so thatthe spring progression value is lower) and better hysteresis propertiesassociated therewith, to select gas springs having the largest possiblecylinder diameters.

A further preferred embodiment of a gas spring designed specifically forthe desired applications has the smallest possible outside diameter forthe piston rod. This design feature once again makes it possible toimprove the hysteresis properties and, most of all, to lower the staticfriction, in particular the necessary “breakaway” force, at the cost ofan increase in dynamic friction.

A further action that, according to the present invention, improves thegas spring is to bore out the nozzles in the piston. In conventional gassprings the diameter of these nozzles is in the range of tenths of amillimeter; in novel fashion, however, it is increased to no less than 2mm, preferably 4 mm. Static friction is thereby minimized.

It is furthermore preferred for the horizontal support to have a longerprotrusion than in the case of conventional stands (900 mm instead of700 mm). Assuming pivot angles at the articulation point of the supportgas spring that are kept small or at the same magnitude, this feature,results not only in a larger pivot range for the load (surgicalmicroscope) in the vertical, but also a larger radius of action.

A preferred embodiment of a stand according to the present inventionadditionally comprises a displacement apparatus for the articulationpoint of the gas spring. This displacement apparatus can be, as knownfrom the existing art, a threaded spindle having a carriage with a guideand a joint, which spindle is driven manually or in motorized fashion.Reference is explicitly made to the possibility of combining thisApplication with an invention filed simultaneously by the sameApplicant, in which a bidirectionally acting displacement apparatus isdisclosed that can also be utilized in the context of the standdisclosed here.

The horizontal support of a stand such as the one used for surgicalmicroscopes is usually configured as a parallelogram support. Horizontalsupports of single configuration are also, however, within the scope ofthe invention.

As already mentioned, the energy storage element can be a gas spring.Also conceivable in general, however, are pneumatic or hydraulic or evenmechanical springs, or combinations thereof.

The invention is moreover not limited to a stand having only one energystorage element; stand solutions having two or more energy storageelements are also intended to fall within the scope of the disclosure ofthis Application, especially with regard to an improvement in hysteresisproperties.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the invention are shown in the Figures. Theinvention will be explained in more detail, symbolically and by way ofexample, with reference to the Figures. The Figures are describedcontinuously and in overlapping fashion. Identical reference charactersdenote identical components; reference characters having differentindices indicate similar or functionally identical components. In thedrawings:

FIG. 1 shows a stand configuration according to the existing art;

FIG. 2 shows a stand arrangement according to the present invention;

FIGS. 3 a-3 c schematically depict the so-called “cosine effect” inthree different positions; and

FIG. 4 shows the spring force diagram of an energy storage elementaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically depicts a stand arrangement 1 according to theexisting art. Stand 1 comprises a vertical support 2 and a horizontalsupport 4 that is implemented as a parallelogram support having an upperhorizontal support arm 4 a and a lower horizontal support arm 4 b. A gasspring is arranged, as a supporting energy storage element 7, at anarticulation point 10 on upper horizontal support arm 4 a of horizontalsupport 4 and at an articulation point 9 in a plate 6. Stand 1 has, as ameans for positively influencing hysteresis properties, a displacementapparatus 18 that does not act linearly but instead permits, by way ofan arc-shaped elongated guide hole 8, a radial displacement ofarticulation point 9.

Gas spring 7 is arranged with a cylinder 12 at distal articulation point10 and with a piston rod 11 at articulation point 9.

This stand arrangement furthermore comprises joints 3 a-d and amicroscope carrier 5. Horizontal support 4 pivots about pivot axis 13,and in turn describes a movement arc 14 in the context of verticalpivoting movements.

FIG. 2 shows a stand arrangement 1 according to the present inventionthat, like the embodiment according to the existing art depicted in FIG.1, comprises a vertical support 2 and a horizontal support 4 implementedas a parallelogram support. In addition, this stand arrangement 1 alsocomprises a displacement apparatus 18′ having a threaded spindle 15which is manually rotatable by rotating a hand knob 17 to cause linearmovement of a threadably mated carriage 16 on which proximalarticulation point 9 is arranged. A guide 19 prevents rotation ofcarriage 16 so that it moves along tspindle 15 when the spindle isrotated. Rotation of spindle 15 may also be controlled by a motor (notshown). As is evident from this Figure, energy storage element 7 isattached with piston rod 11 at an articulation point 10′ that is locatedat the outermost possible distal attachment point of upper horizontalsupport arm 4 a of horizontal support 4. It is also apparent that energystorage element 7 not only is longer but also has a larger cylinderdiameter, and is attached at proximal articulation point 9′ not with itspiston rod 11, but with cylinder 12. Cylinder 12 has an outside diameterpreferably within a range from 10 mm to 100 mm, and most preferably theoutside diameter of cylinder 12 is about 40 mm. The outside diameter ofpiston rod 11 is kept small, preferably within a range from 5 mm to 50mm, and most preferably the outside diameter of piston rod 11 is about14 mm.

FIGS. 3 a-c schematically depict the lever effect as a function ofvarious angles of the horizontal support with respect to the verticalsupport (the so-called “cosine effect”). FIG. 3 a shows horizontal arm 4in a horizontal position (angle between vertical support 2 andhorizontal arm 4=90 degrees). Horizontal arm 4 carries load G at thedistal end and corresponds in this position to lever arm L, and theforce F with which energy storage element 7 braces lever arm L islocated at a (virtual) distance H from articulation point 20 ofhorizontal support 4 on vertical support 2. In this position, L*G=H*F.FIG. 3 b shows horizontal arm 4 in a position pivoted up through anangle α₁. Lever arm L₁ now corresponds to L/cos α₁, and L₁*G is nowequal to H₁*F₁. FIG. 3 c shows horizontal arm 4 in a position pivoteddownward through an angle α₂. Lever arm L₂ now corresponds to L/cos α₂,and the applicable equation is L₂*G=H₂*F₂.

FIG. 4 shows the spring force diagram of an energy storage elementaccording to the present invention. The dynamic hysteresis is thedifference F₃−F₁ or F₄−F₂. The difference in static breakaway force(static hysteresis) at a travel point s₁ between insertion force F₃′ andextension force F₁′, or between F₄′ and F₂′, is less than 60 N accordingto the present invention, as can be read off on the force axis. Theparameters of energy storage element 7 are selected, according to thepresent invention, in such a way that the spring progression is lessthan 10%, preferably 9%. The spring progression is represented on thespring force diagram as the slope from F₁ to F₂ and from F₃ to F₄.

PARTS LIST

The Parts List is a constituent of the disclosure.

-   1 Stand-   2 Vertical support-   3 a-d Joint-   4 Horizontal support-   4 a Upper horizontal support arm-   4 b Lower horizontal support arm-   5 Microscope carrier-   6 Plate-   7 Energy storage element-   8 Arc-shaped elongated guidance hole-   9 Proximal articulation point-   10 Distal articulation point-   11 Piston rod-   12 Cylinder-   13 Pivot axis of 4-   14 Movement arc of load-   15 Threaded spindle-   16 Carriage-   17 Hand knob-   18 Displacement apparatus-   18′ Displacement apparatus-   19 Guide of 16-   20 Articulation point of 4 on 2-   α_(1, 2) Angle between 4 and L_(1, 2)-   L Lever arm-   G Load; weight-   F Force-   H Height; distance of 7 from 20-   s₀ Maximum linear stroke of 11-   s_(1, 2) Travel point of 11 at which measurement occurs-   s₃ End point-   F₁ Extension force at s₀-   F₂ Extension force at s₃-   F₃ Insertion force at s₀-   F₄ Insertion force at s₃-   F₁′ Extension force at s₁-   F₂′ Extension force at s₂-   F₃′ Insertion force at s₁-   F₄′ Insertion force at s₂

1. A stand for a surgical microscope, the stand comprising: a verticalsupport; a horizontal support articulated on the vertical support; andan energy storage element articulated at a proximal articulation pointon the vertical support and at a distal articulation point on thehorizontal support, wherein the energy storage element has a springprogression of less than 10% and is arranged such that the staticfriction associated with movement of the horizontal support is less than60 N.
 2. The stand as defined in claim 1, wherein the spring progressionis less than 9%.
 3. The stand as defined in claim 1, further comprisinga displacement apparatus mounted on the vertical support for changingthe position of the proximal articulation point.
 4. The stand as definedin claim 3, wherein the displacement apparatus includes a threadedspindle and a carriage threadably mated with the spindle to move alongthe spindle upon rotation of the spindle, and wherein the proximalarticulation point is located on the carriage to move therewith.
 5. Thestand as defined in claim 1, wherein the horizontal support isconfigured as a parallelogram support.
 6. The stand as defined in claim1, wherein the horizontal support has a protrusion distance from thevertical support within a range from 500 mm to 1500 mm.
 7. The stand asdefined in claim 6, wherein the protrusion distance is approximately 900mm.
 8. The stand as defined in claim 1, wherein the distal articulationpoint is located near a distal end of the horizontal support.
 9. Thestand as defined in claim 1, wherein the energy storage element includesa gas spring apparatus.
 10. The stand as defined in claim 9, wherein thegas spring apparatus is a pneumatic spring apparatus.
 11. The stand asdefined in claim 1, wherein the energy storage element includes ahydraulic spring apparatus.
 12. The stand as defined in claim 1, whereinthe energy storage element includes a mechanical spring.
 13. The standas defined in claim 1, wherein the energy storage element includes acylinder articulated on the vertical support and a piston rodarticulated on the horizontal support.
 14. The stand as defined in claim1, wherein the energy storage element is a gas spring including acylinder having an outside diameter within a range from 10 mm to 100 mm.15. The stand as defined in claim 14, wherein the outside diameter ofthe cylinder is approximately 40 mm.
 16. The stand as defined in claim1, wherein the energy storage element is a gas spring including a pistonrod having an outside diameter within a range from 5 mm to 50 mm. 17.The stand as defined in claim 16, wherein the outside diameter of thepiston rod is approximately 14 mm.
 18. The stand as defined in claim 1,wherein the energy storage element is a gas spring having a cylinder anda piston within the cylinder, wherein the piston includes nozzleorifices having a diameter of at least 2 mm.
 19. The stand as defined inclaim 18, wherein the piston includes nozzle orifices having a diameterof approximately 4 mm.